Log Message:
Update cyrus-imapd to 2.3.16.

Changes to the Cyrus IMAP Server since 2.3.15

      * Added user_deny.db to be able to selectively deny users access to
        Cyrus services. 
      * Added disconnect_on_vanished_mailbox option. See imapd.conf(5) for
        details 
      * Reworked SQL detection code in configure. See install-upgrade.html
        for more details. 
      * Added popuseimapflags option which enables setting and obeying IMAP
        flags in the POP server. 
      * Added optimized method of handling an empty maildrop in pop3d.